Using mammalian cells cultured in vitro, biological intercomparisons will be made of the fast neutron beams currently used for radiotherapy or planned for future use. This will include the Cleveland Clinic, TAMVEC, NRL, and the Fermilab. Measurements of the oxygen enhancement ratio as a function of neutron energy will be continued at Brookhaven National Laboratory and at the University of Maryland Cyclotron. The biological characterization of heavy ion beams generated by the BEVALAC at the Lawrence Berkeley Laboratory will be initiated.